Substituted 1,4-dihydro-4-oxoquinoline-3-carboxylic acid derivatives (hereinafter quinolones) are known to be effective antibacterial agents (see, for example, U.S. Pat. No. 4,730,000, issued Mar. 8, 1988 to Chu). Halo-substituted benzoic acids and their corresponding esters and acetophenones are useful as starting materials in the synthesis of such quinolones, as disclosed in the published European patent application of Kumai et al., No. 0 303 291, published Feb. 15, 1989.
In particular, 2-chloro-4,5-difluorobenzoic acid (CDFBA), 2,4,5-trifluorobenzoic acid (TFBA), and their respective analogous acetophenones are advantageous starting materials for quinolone synthesis. Known methods of preparing these compounds, however, suffer from a number of drawbacks, including complex chemistry requiring specialized equipment; expensive or hard-to-obtain starting materials; materials hazards such as those associated with the use and decomposition of diazonium salts; and reactions having commercially undesirable selectivities and/or yields. There is therefore a continuing need for an improved process for preparing the above intermediates which overcomes some or all of these disadvantages.